(1) Field of the Invention
The present invention relates to a built-in amplifier type combustion pressure sensor, and more particularly to a built-in amplifier-type combustion pressure sensor in which an assembling operation thereof can be improved.
(2) Description of the Related Art
As a conventional built-in amplifier type combustion pressure sensor, for example, there is suggested a pressure sensor in the Japanese Laid-Open Patent Application No. 63-73648. The sensor disclosed in the Patent Application is provided with a piezoelectric element, which is a pressure detecting portion, on one end of a cylindrical sensor body. The sensor is also provided with a circuit board, on which an amplifier circuit amplifying signals provided by the piezoelectric element is formed. The piezoelectric element is located within the sensor body oriented such that a surface of the circuit board is situated parallel to an axis of the sensor body. Lead wires extended from the piezoelectric element run through from one end of the sensor body to the circuit board along an axial direction of the sensor body and the lead wires are connected to one end of the circuit board. Output lead wires are connected to the other end of the circuit board, which is at the opposite end of the piezoelectric circuit.
The above mentioned conventional sensor is assembled with a separately prepared piezoelectric element, sensor body and a cover that covers the circuit board. After connecting the lead wires from the piezoelectric element to the circuit board and connecting the output lead wires to the circuit board, the cover is assembled in place inside the sensor body. An alternate method is integrally forming the sensor body and the cover; pulling out the lead wires extended from the piezoelectric element and connecting the lead wires and the output lead wires to the circuit board; inserting the circuit board into the cover by placing the lead wires from the piezoelectric element inside the cover.
In the first assembling method, it is a troublesome matter to insert and fix the circuit board, which board which has already been connected to the lead wires, to the sensor body. In the second assembling method, a great care must be taken when inserting the lead wires into the cover of the sensor body so as to prevent the lead wires from contacting and damaging component parts on the circuit board. Thus, the conventional built-in amplifier-type combustion pressure sensor has a problem in that the assembling operation is not effectively conducted.